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.TH SETJMP 3C "Aug 14, 2002"
.SH NAME
setjmp, sigsetjmp, longjmp, siglongjmp \- non-local goto
.SH SYNOPSIS
.LP
.nf
#include <setjmp.h>

\fBint\fR \fBsetjmp\fR(\fBjmp_buf\fR \fIenv\fR);
.fi

.LP
.nf
\fBint\fR \fBsigsetjmp\fR(\fBsigjmp_buf\fR \fIenv\fR, \fBint\fR \fIsavemask\fR);
.fi

.LP
.nf
\fBvoid\fR \fBlongjmp\fR(\fBjmp_buf\fR \fIenv\fR, \fBint\fR \fIval\fR);
.fi

.LP
.nf
\fBvoid\fR \fBsiglongjmp\fR(\fBsigjmp_buf\fR \fIenv\fR, \fBint\fR \fIval\fR);
.fi

.SH DESCRIPTION
.sp
.LP
These functions are useful for dealing with errors  and interrupts encountered
in a low-level subroutine of a program.
.sp
.LP
The \fBsetjmp()\fR function saves its stack environment in \fIenv\fR for later
use by \fBlongjmp()\fR.
.sp
.LP
The \fBsigsetjmp()\fR function saves the calling process's registers and stack
environment (see \fBsigaltstack\fR(2)) in  \fIenv\fR for later use by
\fBsiglongjmp()\fR. If  \fIsavemask\fR is non-zero, the calling process's
signal mask (see \fBsigprocmask\fR(2)) and scheduling parameters (see
\fBpriocntl\fR(2)) are also saved.
.sp
.LP
The \fBlongjmp()\fR function restores the environment saved by the last call of
\fBsetjmp()\fR with the corresponding \fIenv\fR argument. After \fBlongjmp()\fR
completes, program execution continues as if the corresponding call to
\fBsetjmp()\fR had just returned the value \fIval\fR. The caller of
\fBsetjmp()\fR must not have returned in the interim.  The \fBlongjmp()\fR
function cannot cause \fBsetjmp()\fR to return the value 0.  If \fBlongjmp()\fR
is invoked with a second argument of 0, \fBsetjmp()\fR will return 1. At the
time of the second return from \fBsetjmp()\fR, all external and static
variables have values as of the time \fBlongjmp()\fR is called (see
\fBEXAMPLES\fR).
.sp
.LP
The \fBsiglongjmp()\fR function restores the environment saved by the last call
of \fBsigsetjmp()\fR with the corresponding \fIenv\fR argument. After
\fBsiglongjmp()\fR completes, program execution continues as if the
corresponding call to \fBsigsetjmp()\fR had just returned the value \fIval\fR.
The \fBsiglongjmp()\fR function cannot cause \fBsigsetjmp()\fR to return the
value 0.  If \fBsiglongjmp()\fR is invoked with a second argument of 0,
\fBsigsetjmp()\fR will return 1. At the time of the second return from
\fBsigsetjmp()\fR, all external and static variables have values as of the time
\fBsiglongjmp()\fR was called.
.sp
.LP
If a signal-catching function interrupts \fBsleep\fR(3C) and calls
\fBsiglongjmp()\fR to restore an environment saved prior to the \fBsleep()\fR
call, the action associated with \fBSIGALRM\fR and time it is scheduled to be
generated are unspecified. It is also unspecified whether the \fBSIGALRM\fR
signal is blocked, unless the process's signal mask is restored as part of the
environment.
.sp
.LP
The  \fBsiglongjmp()\fR function restores the saved signal mask if and only if
the  \fIenv\fR argument was initialized by a call to the \fBsigsetjmp()\fR
function with a non-zero  \fIsavemask\fR argument.
.sp
.LP
The values of register and automatic variables are undefined. Register or
automatic variables whose value must be relied upon must be declared as
volatile.
.SH RETURN VALUES
.sp
.LP
If the return is from a direct invocation, \fBsetjmp()\fR and \fBsigsetjmp()\fR
return \fB0\fR. If the return is from a call to \fBlongjmp()\fR, \fBsetjmp()\fR
returns a non-zero value. If the return is from a call to \fBsiglongjmp()\fR,
\fBsigsetjmp()\fR returns a non-zero value.
.sp
.LP
After \fBlongjmp()\fR is completed, program execution continues as if the
corresponding invocation of \fBsetjmp()\fR had just returned the value
specified by \fIval\fR. The \fBlongjmp()\fR function cannot cause
\fBsetjmp()\fR to return 0; if \fIval\fR is 0, \fBsetjmp()\fR returns 1.
.sp
.LP
After \fBsiglongjmp()\fR is completed, program execution continues as if the
corresponding invocation of \fBsigsetjmp()\fR had just returned the value
specified by \fIval\fR. The \fBsiglongjmp()\fR function cannot cause
\fBsigsetjmp()\fR to return 0; if \fIval\fR is 0, \fBsigsetjmp()\fR returns 1.
.SH EXAMPLES
.LP
\fBExample 1 \fRExample of \fBsetjmp()\fR and \fBlongjmp()\fR functions.
.sp
.LP
The following example uses both \fBsetjmp()\fR and \fBlongjmp()\fR to return
the flow of control to the appropriate instruction block:

.sp
.in +2
.nf
#include <stdio.h>
#include <setjmp.h>
#include <signal.h>
#include <unistd.h>
jmp_buf env; static void signal_handler();

main(\|)  {
        int returned_from_longjump, processing = 1;
        unsigned int time_interval = 4;
        if ((returned_from_longjump = setjmp(env)) != 0)
            switch (returned_from_longjump)     {
              case SIGINT:
                printf("longjumped from interrupt %d\en",SIGINT);
                break;
              case SIGALRM:
                printf("longjumped from alarm %d\en",SIGALRM);
                break;
            }
        (void) signal(SIGINT, signal_handler);
        (void) signal(SIGALRM, signal_handler);
        alarm(time_interval);
        while (processing)        {
          printf(" waiting for you to INTERRUPT (cntrl-C) ...\en");
          sleep(1);
        }		 /* end while forever loop */
}

static void signal_handler(sig)
int sig; {
        switch (sig)     {
          case SIGINT:	... 	  /* process for interrupt */
                      	longjmp(env,sig);
                             	  /* break never reached */
          case SIGALRM:	... 	  /* process for alarm */
                       	longjmp(env,sig);
                               /* break never reached */
          default:     	exit(sig);
        }
}
.fi
.in -2

.sp
.LP
When this example is compiled and executed, and the user sends an interrupt
signal, the output will be:

.sp
.in +2
.nf
longjumped from interrupt
.fi
.in -2
.sp

.sp
.LP
Additionally, every 4 seconds the alarm will expire, signalling this process,
and the output will be:

.sp
.in +2
.nf
longjumped from alarm
.fi
.in -2
.sp

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	Unsafe
.TE

.SH SEE ALSO
.sp
.LP
.BR getcontext (2),
.BR priocntl (2),
.BR sigaction (2),
.BR sigaltstack (2),
.BR sigprocmask (2),
.BR signal (3C),
.BR attributes (7),
.BR standards (7)
.SH WARNINGS
.sp
.LP
If \fBlongjmp()\fR or \fBsiglongjmp()\fR are called even though \fIenv\fR was
never primed by a call to \fBsetjmp()\fR or \fBsigsetjmp()\fR, or when the last
such call was in a function that has since returned, the results are undefined.
